title: Risk factors for aseptic loosening of Müller-type straight stems: a registry-based analysis of 828 consecutive cases with a minimum follow-up of 16 years.
abstract: Background and purpose Even small differences in design variables for the femoral stem may influence the outcome of a hip arthroplasty. We performed a risk factor analysis for aseptic loosening of 4 different versions of cemented Müller-type straight stems with special emphasis on design modifications (2 shapes, MSS or SL, and 2 materials, CoNiCrMo (Co) or Ti-6Al-7Nb (Ti)). Methods We investigated 828 total hip replacements, which were followed prospectively in our in-house register. All stems were operated in the same setup, using Sulfix-6 bone cement and a second-generation cementing technique. Demographic and design-specific risk factors were analyzed using an adjusted Cox regression model. Results The 4 versions showed marked differences in 15-year stem survival with aseptic loosening as the endpoint: 94% (95% CI: 89-99) for MSS Co, 83% (CI: 75-91) for SL Co, 81% (CI: 76-87) for MSS Ti and 63% (CI: 56-71) for SL Ti. Cox regression analysis showed a relative risk (RR) for aseptic loosening of 3 (CI: 2-5) for stems made of Ti and of 2 (CI: 1-2) for the SL design. The RR for aseptic stem loosening increased to 8 (CI: 4-15) when comparing the most and the least successful designs (MSS Co and SL Ti). Interpretation Cemented Müller-type straight stems should be MSS-shaped and made of a material with high flexural strength (e.g. cobalt-chrome). The surface finish should be polished (Ra < 0.4 µm). These technical aspects combined with modern cementing techniques would improve the survival of Müller-type straight stems. This may be true for all types of cemented stems.
authors.affiliation: Clinic for Orthopedic and Trauma Surgery, Kantonsspital Baselland Liestal, Switzerland. martin.clauss@ksli.ch
authors.forename: Martin
authors.initials: M
authors.lastname: Clauss
authors.forename: Silke
authors.initials: S
authors.lastname: Gersbach
authors.forename: Andre
authors.initials: A
authors.lastname: Butscher
authors.forename: Thomas
authors.initials: T
authors.lastname: Ilchmann
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006622:Hip Prosthesis / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011446:Prospective Studies; D011474:Prosthesis Design / Q000706:statistics & numerical data*; D011475:Prosthesis Failure; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D016896:Treatment Outcome